The present invention relates to a method for forming a moisture barrier or a water-impermeable layer in a soil containing soluble salts and/or exchangeable cations or, more particularly, to a method in which a soil containing soluble salts and/or exchangeable cations is treated with an aqueous solution containing a water-soluble polymeric material so as to form a water-impermeable layer at a desired depth with an object to save the volume of water for irrigation on a sandy land, to prevent adverse influences by salinity in an arid or semi-arid land and to prevent water leakage in a dam or bank of water reservoir.
It is known and widely practiced in soil engineering that a moisture barrier or a layer impermeable to underground water is provided at a certain depth in the soil with an object to prevent loss of water of irrigation by infiltration into depth of the soil in a sandy land, to prevent adverse influences on the growth of plants caused by the salinity which has been brought up to and accumulated in the surface layer of the soil as being dissolved in and carried by the underground water rising from the depth to the surface along with the water evaporation in the daytime and to prevent water leakage in a dam or bank of water reservoir.
Such a water-impermeable layer in the soil is provided in the prior art in several different means including a sheet of a plastic resin spread underground over the whole area of the land as desired, a layer of asphalt in place of the plastic sheet and a coagulated layer of a soil-treatment agent such as a cement milk, water glass, urethane, acrylamide, salt of acrylic acid and the like in a liquid form which is injected into the soil by pressurization through a nozzle inserted into the soil where the agent is reacted and coagulated.
These prior art methods are, however, each not fully practicable due to the disadvantages and problems in one or more respects. For example, the methods using a plastic sheet or asphalt are applicable only to a relatively small land since the soil over the land must be wholly lifted and returned after the plastic sheet or the asphalt layer has been spread taking a great deal of time and labor rendering the method almost inapplicable to a large land. The method relying on the soil-treatment agent injected into the soil is not free from the troublesome preparation of the liquid agent and necessity of delicately controlling the conditions of the injection thereof. Moreover, the effectiveness of injection is limited to the very vicinity of the injection spot so that the injection should be performed at as many spots as possible in order not to leave any area untreated.
An efficient method has been proposed in Japanese Patent Kokai No. 59-202287 by the inventor together with coinventors for the formation of a water-impermeable layer in the soil by sprinkling an aqueous solution of a water-soluble polymeric material over the land so that the solution infiltrates the soil where the polymer is converted into a water-insoluble form to provide a water-impermeable layer. A problem in this method is, however, that the depth in the soil where the water-impermeable layer is formed by the insolubilization of the polymer is greatly influenced by the nature of the soil and subject to uncontrollable variation so that the advantage to be obtained by the water-impermeable layer in the soil cannot be so high as desired. Moreover, the thus formed water-impermeable layer not always has a strength high enough. The problem of the uncontrollable depth of the water-impermeable layer formed in the soil is even more serious when the soil contains a relatively large amount of soluble cations in excess of, for example, 10 meq per 100 g of dry soil.